This application is related to Japanese patent application No. HEI 10-178948 filed on Jun. 25, 1998 whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a file data retrieving device and a recording medium containing a computer program for controlling the same, and more particularly to a file data retrieving device and a recording medium for use thereof which are applied to a document processing apparatus, such as a word processor or a personal computer, for retrieving a specific file data from a plurality of encoded file data stored in a storage device.
2. Description of the Related Art
In recent years, in accordance with a spread of word processors and personal computers, a large amount of document data are utilized at a place of work or at home. Large-capacity databases and high speed retrieving machines have been studied and developed in order to rearrange and utilize a large amount of such document data effectively.
In the meantime, a document that must maintain its secrecy is stored in a database in a form encoded by cryptography.
As a file retrieval method that does not use cryptography, there are known, for example, a full text search method and a key word search method.
For example, as a full text search method, Japanese Unexamined Patent Publication No. HEI 05(1993)-101102 proposes a retrieving device that enables effective retrieval by reducing the volume of the file to be used for presearch in the full text search on the basis of the full text search method by which the required document data are drawn out from a secondary storage device that stores a large amount of document data without giving index information for retrieval.
On the other hand, as a key word search method, Japanese Unexamined Patent Publication No. HEI 09(1997)-44521 proposes an index making device and a document retrieving device for specifying a document by registering, as a common identifier (i.e., an index), a word selected from a plurality of different representations in registering the documents and comparing an input key word with the index by utilizing the index in the retrieving process.
Further, known cryptography methods include, for example, symmetric cryptography methods and asymmetric cryptography methods.
A symmetric cryptography method is a cryptography method in which the same key is used for encoding and decoding processes. In this method, a cryptography communication is not possible unless the sender and the receiver share a common key data, so that the problem is how the key can be safely shared. This method is referred to as xe2x80x9cprivate key cryptographyxe2x80x9d because the key must be kept secret.
An asymmetric cryptography method is a cryptography method in which different keys are used for an encoding process and a decoding process. This method eliminates the need to share the same information in secret among the communicating parties by making a cryptograph key publicly known and keeping a decoding key retained in secret. This method is referred to as xe2x80x9cpublic key cryptographyxe2x80x9d because one key is made publicly known.
For example, as a symmetric cryptography method, Japanese Unexamined Patent Publication No. HEI 06(1994)-149153 proposes a general-purpose high-speed cryptography device utilizing a FEAL (fast data encipherment algorithm) in which an enlarged key is created by means of an input such as a cryptography key having a 64 bit length and an fk function; the enlarged key is retained; and an input data having a 64 bit length, which is a plaintext or a ciphertext, and the retained enlarged key are encoded or decoded by means of an exclusive logical sum and an f function.
On the other hand, as an asymmetric cryptography method, Japanese Unexamined Patent Publication No. HEI 06(1994)-169306 proposes a protocol and a device in which a message part of a public key distribution method is encoded into asymmetric cryptograph keys and the asymmetric cryptograph keys are exchanged with each other to establish a safe communication among a plurality of parties that share a secret key.
Also, a translated document by Yuu Inamura, xe2x80x9cEncipherment of electronic mails by PGP, S/MIME, Japanese version of DDJ, February 1998 (magazine code 16665-02)-, Author""s preface to the book: xe2x80x9cPGP Source Code and Internalsxe2x80x9d, by Philip Zimmermann ISBN 0-262-24039-4)xe2x80x9d discloses a cryptography processing of PGP (Pretty Good Privacy).
This PGP method uses a symmetric cryptography and an asymmetric cryptography in combination, whereby after an extra key data which differs for each encoding process is created to encode a message body in a symmetric manner, the extra key itself is encoded in an asymmetric manner by using a public key of a receiver, and both of the encoded message body and the encoded extra key are sent to the receiver. The receiver of the message decodes the extra key by means of the receiver""s secret key and then decodes the extra key by means of the receiver""s secret key and then decodes the message body by means of the extra key thus decoded.
However, the full text search method disclosed in Japanese Unexamined Patent Publication NO. HEI 05(1993)-101102 and the key word search method disclosed in Japanese Unexamined Patent Publication No. HEI 09(1997)-44521 are directed to plaintexts which are not encoded, and it is not possible to directly search for document data that are stored in an encoded form.
Therefore, in the above-mentioned full text search method, the searching process must be carried out after all the encoded document data are decoded. This necessitates an enormous amount of processing in order to make a search among the document data existing in a large amount, thus requiring an extra management in order to safely maintain secrecy of the document data.
Further, in the above-mentioned key word search method, it is possible to search for a document file if all the document data are decoded to make indices and only the key words are stored as plaintexts. However, in this method, the key words are read, whereby the secrecy of the document data is destroyed even though the stored document data are encoded, thus requiring an extra management in order to safely maintain the secrecy of the document data.
The techniques disclosed in Japanese Unexamined Patent Publication No. HEI 06(1994)-149153, Japanese Unexamined Patent Publication No. HEI 06(1994)-169306, and the translated document by Yuu Inamura are directed to an encoding process and a decoding process for establishing a safe communication between parties that share a common secret key, and they do not disclose a technique of searching for a specific file at a high speed from a plurality of encoded file data stored in a storage device.
The present invention provides a file data retrieving device comprising: an input section for inputting a search character string and various instructions; a storage section that previously stores a plurality of encoded file data; a decoding section for decoding the encoded file data by use of a cryptograph key prepared in advance; an extracting section for extracting, from the decoded file data, a file name and a plurality of key words related to the file data; an encoding section for encoding the extracted key words; a storage processing section for allowing the storage section to store the encoded key words as access keys of the file data in correspondence with the stored file data; and a retrieving section for allowing the encoding section to encode the search character string which is input by the input section for retrieving the file name of the encoded file data, searching for an access key that coincides with the encoded search character string, and retrieving the file name that corresponds to the access key.
Also, the present invention provides a recording medium containing a computer program for controlling a file data retrieving device, the computer program performing the functions of: causing a computer operation to input a search character string and various instructions from an input section; causing a computer operation to previously store a plurality of encoded file data in a storage section; causing a computer operation to decode the encoded file data by use of a cryptograph key prepared in advance; causing a computer operation to extract, from the decoded file data, a plurality of key words and a file name related to the file data; causing a computer operation to encode the extracted keywords; causing a computer operation to store the encoded key words as access keys of the file data in the storage section in correspondence with the stored file data; and causing a computer operation to encode the search character string which is input by the input section for retrieving the file name of the encoded file data, to search for an access key that coincides with the encoded search character string, and to retrieve the file name that corresponds to the access key.
Thus, the present invention provides a file data retrieving device and a recording medium for use thereof in which a specific file data is retrieved by use of an encoded key word at a high speed from a plurality of encoded file data stored in a storage device while maintaining secrecy of the file data.